Stent with offset cell geometry

ABSTRACT

A stent defining a longitudinal axis is disclosed. A plurality of circumferential support structures are spaced-apart along the longitudinal axis. At least some of the circumferential support structures are interconnected by connection members that extend generally in a circumferential direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to implants for use in intraluminalapplications. More particularly, this invention pertains to stents foruse in vascular applications.

2. Description of the Prior Art

Stents are widely used for supporting a lumen structure in a patient'sbody. For example, stents may be used to maintain patency of a coronaryartery, other blood vessel or other body lumen.

Commonly, stents are metal, tubular structures. Stents are passedthrough the body lumen in a collapsed state. At the point of anobstruction or other deployment site in a body lumen, the stent isexpanded to an expanded diameter to support the lumen at the deploymentsite.

In certain designs, stents are open-celled tubes that are expanded byinflatable balloons at the deployment site. This type of stent is oftenreferred to as a “balloon expandable” stent and is often made of aplastically deformable material such as stainless steel. Other stentsare so-called “self-expanding” stents. Self-expanding stents do not useballoons to cause the expansion of the stent. An example of aself-expanding stent is a tube (e.g., a coil tube or an open-cell tube)made of an elastically deformable material. Elastically deformableself-expanding stents are typically secured to a stent delivery deviceunder tension in a collapsed state. At the deployment site, the stent isreleased so that internal tension within the stent causes the stent toself-expand to its enlarged diameter. This type of stent is often madeof a “super-elastic” material such as nitinol. Other self-expandingstents are made of so-called shape-memory metals. Such shape-memorystents experience a phase change at the elevated temperature of thehuman body. The phase change results in expansion from a collapsed stateto an enlarged state.

SUMMARY OF THE INVENTION

One embodiment of the present invention relates to a stent having alongitudinal axis. A plurality of circumferential support structures arespaced-apart along the longitudinal axis. At least some of thecircumferential support structures are interconnected by connectionmembers that extend generally in a circumferential direction.

A variety of advantages of the invention will be set forth in part inthe description that follows, and in part will be apparent from thedescription, or may be learned by practicing the invention. It is to beunderstood that both the foregoing general description and the followingdetailed description are exemplary and explanatory only and are notrestricted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a first embodiment of a stent according to thepresent invention as it would appear if it were longitudinally split andlaid out flat.

FIG. 2 is the view of FIG. 1 following expansion of the stent.

FIG. 3 is a partial plan view of a tapered-strut stent according to thepresent invention as it would appear if it were longitudinally split andlaid out flat.

FIG. 4 is a partial plan view of another embodiment of a stent accordingto the present invention as it would appear if it were longitudinallysplit and laid out flat.

FIG. 5 is a partial plan view of another embodiment of a stent accordingto the present invention as it would appear if it were longitudinallysplit and laid out flat.

FIG. 6 is an enlarged partial view of the stent of FIG. 1.

FIG. 7 is a partial plan view of another embodiment of a stent accordingto the present invention, as it would appear if it were longitudinallysplit and laid out flat.

FIG. 8 is a plan view of another embodiment of a stent according to thepresent invention, as it would appear if it were longitudinally splitand laid out flat.

FIG. 9 is a plan view of another embodiment of a stent according to thepresent invention, as it would appear if it were longitudinally splitand laid out flat.

While the invention is amenable to various modifications and alternativeforms, the specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring now to the several drawing figures in which identical elementsare numbered identically, a description of the preferred embodiment ofthe present invention will now be provided. In the following detaileddescription, references are made to the accompanying drawings thatdepict various embodiments in which the invention may be practiced. Itis to be understood that other embodiments may be utilized, andstructural and functional changes may be made without departing from thescope of the present invention. Further, each of the features disclosedherein can be considered stand-alone inventive features or features thathave inventive aspects when considered in combination with one another.

FIG. 1 illustrates a stent 10, shown longitudinally split and laid flat,having an un-deployed or reduced circumference C_(r) and an un-deployedlength L. FIG. 6 is an enlarged partial view of FIG. 1 to betterillustrate a strut geometry as will be described.

The stent 10 is a reticulated, hollow tube. The stent 10 may be expandedfrom the reduced circumference C_(r) to an expanded or enlargedcircumference C_(e). FIG. 2 is a view illustrating the expanded stent 10as it would appear if longitudinally split and laid flat. The enlargedcircumference C_(e) is shown in FIG. 2.

The material of the stent 10 defines a plurality of circumferentialsupport structures 12 spaced apart along the longitudinal axis, X-X ofthe stent 10. The phrase “circumferential support structures” will beunderstood to include structures that extend generally about thecircumference of the stent 10. The support structures 12 are formed bylongitudinal struts 14. In one embodiment, the struts 14 have uniformcross-sectional dimensions throughout their length. Adjacent struts 14within a support structure 12 are connected at apex portions 18 to forman undulating pattern that extends about the circumference of the stent10. As used herein, “apex portion” is intended to mean the region wheretwo struts 14 are joined. The apex portions 18 can be semicircular,arcuate, pointed, square, oval, or any other shape. Adjacent supportstructures 12 are joined by circumferential connecting struts 16 joiningapex portions 18. The phrase “circumferential connecting struts” or“circumferential connecting members” will be understood to mean strutsor members that interconnect adjacent circumferential support structures12 and have a spacial component or vector that extends in acircumferential direction about the stent 12. The struts 14, apexportions 18 and connecting struts 16 form bounded areas, or cells 20,which are open as shown in FIG. 2 (i.e., extend through the wallthickness of the stent 10).

The struts 14 may all be the same length, or they may be of differinglength. In one embodiment, when some longer struts are present, thelonger struts in adjacent support structures interconnected.

The stent 10 may be formed through any suitable means including laser orchemical milling. In such processes, a hollow cylindrical tube laser cutor etched to remove material and form the open cells 20.

In the embodiment of FIG. 1, the struts 14 extend along the longitudinalaxis of the stent in the un-deployed orientation (FIGS. 1 and 6). Atleast some of the apex portions 18 are configured such that, when thestent is in the un-deployed orientation, they overlap in theaxial/longitudinal direction. As used herein. “overlap” is intended tomean the apex portions 18 are directly in line circumferentially or theapex portions 18 extend past each other such that the connecting strutjoining them is positioned at an angle relative to the circumference. Inthe embodiment illustrated in FIGS. 1 and 6, the overlapping apexportions 18 are directly in line circumferentially, and the connectingstruts 16 are substantially perpendicular to the struts 14. In theembodiment illustrated in FIG. 7, apex portions 118 extending past eachother are joined by angled connecting struts 416. The angled connectingstruts 416 extend at an oblique angle with respect to thecircumferential direction.

The embodiment of FIG. 3 includes longitudinal struts 114 that aretapered, as disclosed in co-pending, commonly assigned, U.S. patentapplication Ser. No. 09/765,725, the entire disclosure of which isincorporated herein by reference. In the embodiment illustrated in FIG.3, circumferential support structures 112 are made up of pairs oftapered struts 114 alternating with single, non-tapered struts 113. Thetapered struts 114 are arranged such that their wide ends 115 areadjacent circumferential connecting struts 116 and their narrow ends 117are adjacent unconnected or free apex portions. In a further embodiment,the connecting struts 116 can connect only apex portions 118 joiningnarrow ends 117.

To increase the radiopacity of the stent, one or more of the connectingstruts can have a width greater than the width of the longitudinalstruts 14. In the embodiment illustrated in FIG. 4, all connectingstruts 216 are wide. Preferably, the connecting struts 216 are at least1.25, or 2, or 3, or 4, or 5, or 6, or 7 or 8 times as wide as thestruts 14. By way of example, the connecting struts might range from0.01 inch to 0.050 inches in width. In the embodiment illustrated inFIG. 5, wide connecting struts 216 are positioned between some of thesupport structures 12, and narrower connecting struts 16 are positionedbetween the remaining support structures 12. Incorporating both wideconnecting struts 216 and narrower connecting struts 16 in the stent canprovide a customized radiopacity.

In use, the stent 10 is advanced to a site in a lumen (e.g., anocclusion site in need of circumferential support) while in thecompressed orientation. The stent 10 is then expanded at the site. Thestent 10 may be expanded through any conventional means. For example,the stent 10 in the reduced diameter may be placed at the tip of aballoon catheter. At the site, the stent is expanded (e.g., throughexpansion of the balloon) thereby causing the stent to expand from thecompressed orientation to the deployed orientation. A preferred materialfor balloon expandable stents is stainless steel. For self-expandingstents, the stent 10 may be formed of a super-elastic or shape memorymaterial, such as nitinol, which is an alloy of nickel and titanium.

During expansion of the stent 10, the cells 20 open to a configurationas shown in FIG. 2. The expansion of the stent 10 is typically providedprimarily through bending of the apex portions 18.

The stent 10 is highly flexible. To advance to a site, the axis X-X ofthe stent 10 bends to navigate trough a curved lumen. Further, forplacement at a curved site in a lumen, the stent 10 is preferablysufficiently flexible to retain a curved shape following expansion andto bend as the lumen bends over time. The stent 10, as described above,achieves these objections.

When bending on its axis X-X, the stent 10 tends to axially compress onthe inside of the bend and axially expand on the outside of the bend.The present design permits such axial expansion and contraction. Thecell geometry results in a structure that is highly flexible before andafter radial expansion.

When the stent 10 is in the deployed orientation, as shown in FIG. 2,the apex portions 18 on adjacent support structures 12 are offset. Whenthe stent 10 flexes and to bends, the apex portions 18 and correspondingstruts 14 on one support structure 12 do not come in direct contact withfacing apex portions 18 and struts 14 on an adjacent support structure12. This offset geometry provides increased flexibility to the stent 10and allows the stent 10 to better conform to a lumen such as a coronaryvessel.

In one embodiment, as shown in FIG. 2, the distance of offset D₁provided by the connection member 16 is about one-half the distance D₂provided between the apex portions 18 (i.e., D₁=0.5D₂). Thus, adjacentcircumferential support structures 12 define waves that are “in-phase”with one another. This provides a greater longitudinal spacing (i.e., ina direction corresponding to the longitudinal axis of the stent) betweenthe peaks as compared to having the apexes being in direct opposition toone another.

Table 1 provides examples of stent diameters and examples of offsetgeometry based on the number of apex portions around the circumferenceof the stent. It is to be understood that the dimensions in Table 1 areexemplary only and are not intended to be limiting. The dimensions areapplicable to a stent in the expanded or deployed orientation. The stentdimensions will be selected based on the size and location of the lumeninto which the stent is to be placed. This offset geometry allows forflexion of the stent without adjacent struts directly impacting eachother. The preferred geometry has the apexes of struts in one supportstructure in between the apexes of struts in the adjacent supportstructure. When the stent is flexed, the apexes pass by one another anddo not impact, which allows for increased flexibility.

TABLE I Number of Preferred Offset: I.D. I.D. apexes Distance between ½distance between Dia- Dia- Circum- around apexes around apexes aroundmeter meter ference Circum- Circumference Circumference (mm) (inch)(inch) ference (inch) (inch) 6.25 0.246 0.773 18 0.043 0.021 7.25 0.2850.897 18 0.050 0.025 8.25 0.325 1.020 18 0.057 0.028 9.25 0.364 1.144 180.064 0.032

Numerous modifications are possible. For example the stent 10 may belined with either an inner or outer sleeve (such as polyester fabric orePTFE) for tissue growth. Also, the stent may be coated with radiopaquecoatings such as platinum, gold, tungsten or tantalum. In addition tomaterials previously discussed, the stent may be formed of any one of awide variety of previous known materials including, without limitation,MP35N, tantalum, platinum, gold, Elgiloy and Phynox.

While twenty support structures 12 are shown in FIGS. 1 and 2 connectedand spaced apart along the longitudinal axis of the stent, a differentnumber could be so connected to vary the properties of the stent 10 as adesigner may elect. Likewise, while each support structure 12 in FIGS. 1and 2 is shown as having 36 struts 14, the number of struts 14 couldvary to adjust the properties of the stent. Also, while each supportstructure 12 is shown connected to an adjacent support structure 12 by 6connecting struts 16, the number of connecting struts 16 could vary. Inone embodiment, the stent is made up of 20 support structures, 36 strutsper support structure, 18 apex portions on each side of each supportstructure, and 6 connecting struts joining every third apex portion ofadjacent support structures. Alternating the direction of the connectingstruts between support structures prevents uneven expansion anglesbetween the struts and prevents twisting of the stent. For example, inFIG. 1, connecting struts 16 extend from one apex portion 18 down toanother apex portion 18 between first and second support structures, andextend up between the second and third support structures. Thisalternating pattern of connecting struts is more pronounced in theembodiment with angled connecting struts 416, shown in FIG. 7.

When forming the stent from shape memory metal such as nitinol, thestent can be laser cut from a nitinol tube. Thereafter, the stent can besubjected to a shape-setting process in which the cut tube is expandedon a mandrel and then heated. Multiple expansion and heating cycles canbe used to shape-set the stent to the final expanded diameter.

In use, the finished stent can be mounted on a delivery catheter. As isconventionally known in the art, the stent can be held in a compressedorientation on the to delivery catheter by a retractable sheath. As isalso known in the art, the delivery catheter can be used to advance thestent to a deployment location (e.g., a constricted region of a vessel).At the deployment cite, the sheath is related thereby releasing thestent. Once released, the stent self-expands to the deployed diameter.

FIG. 8 shows another stent 510 that is another embodiment of the presentis invention. The stent 510 is shown in a configuration corresponding tothe stent when the stent has been initially fabricated from a tube(i.e., before the stent has been compressed on a catheter). Similar tothe previous embodiments, the stent is shown longitudinally split andlaid flat for ease of explanation. The stent includes 10 circumferentialsupport structures CS1-CS10 spaced-apart along a longitudinal axis LA ofthe stent 510. Longitudinal struts 14 and apex portions 18 of thesupport structures CS1-CS10 define an undulating pattern that extendsabout the circumference of the stent 510. The undulating pattern definesa wave having a wavelength WL. Alternating pairs of the adjacent supportstructures are interconnected by circumferential connecting struts 16.For example, support structure pairs CS2 and CS3; CS4 and CS5; CS6 andCS7; and CS8 and CS9 are interconnected by circumferential connectingstruts 16. Struts 16 interconnecting structure CS2 to structure CS3 andstructure CS6 to structure CS7 extend downwardly, and struts 16interconnecting structure CS4 to structure CS5 and structure CS8 tostructure CS9 extend upwardly. By alternating the direction ofextension, uniform expansion is facilitated.

Circumferential support structures CS1 and CS2; CS3 and CS4; CS5 andCS6; CS7 and CS8; and CS9 and CS10 are not interconnected bycircumferential connecting struts. Instead, these pairs are integrallyconnected to one another.

Referring again to FIG. 8 , the circumferential connecting struts 16function to offset the apexes 18 of adjacent circumferential supportstructures relative to one another so that the apexes do not oppose oneanother. By offsetting the apex portions that face toward one another,the tips are prevented from contacting one another when in the expandedstate thereby enhancing the stent's ability to conform to a lumen inwhich the stent is implanted. In the depicted embodiment, thecircumferential connecting struts 16 have a length equal to about oneand one half (i.e., 1.5) wavelengths WL. Preferably, the circumferentialstruts 16 have a length of at least one half (i.e., 0.5) the wavelengthWL. The integrally connected pairs of circumferential support structureshave apex portions 18 that oppose one another.

FIG. 9 shows a stent 610 that is another embodiment of the presentinvention. The stent 610 is shown in a configuration corresponding tothe stent when the stent has been initially fabricated from a tube(i.e., before the stent has been compressed on a catheter). Similar tothe previous embodiments, the stent is shown longitudinally split andlaid flat for ease of explanation. The stent includes 10 circumferentialsupport structures CS1-CS10 spaced-apart along a longitudinal axis LA ofthe stent 610. Longitudinal struts 14 and apex portions 18 of thesupport structures CS1-CS10 define an undulating pattern that extendsabout the circumference of the stent 510. Support structure pairs CS2and CS3; CS3 and CS4; CS7 and CS8, and CS8 and CS9 are interconnected bycircumferential connecting members 16. The remaining support structurepairs (i.e., pairs CS1 and CS2; CS4 and CS5; CS5 and CS6; CS6 and CS7;and CS9 and CS10) are interconnected by integrally.

In the embodiments of FIGS. 8 and 9, the circumferential connectingstruts 16 are generally perpendicularly aligned relative to the apexportions 18. In other embodiments, the circumferential connecting struts16 could be angled similar to the struts 416 of FIG. 7. In embodimentswhere the apex portions 18 are not longitudinally overlapped, thecircumferential connecting struts could be angled in the oppositedirection as compared to the struts 416 of FIG. 7.

While a preferred use for the inventive features disclosed in FIGS. 1-9is in a self-expanding stent, the features also have benefits when usedwith non-self-expanding stents (e.g., balloon expandable stents made ofa material such as stainless steel). Also, while FIGS. 1-9 illustrate apreferred geometry for practicing the present invention, the techniquefor avoiding opposing longitudinal members coming in direct contact byvarying the offset positions of the struts and apex positions in a stentis also applicable to stents having other geometries, shapes, or strutpatterns.

From the foregoing, the present invention has been shown in a preferredembodiment. Modifications and equivalents are intended to be includedwithin the scope of the appended claims.

1. A stent comprising: a stent body expandable between an un-deployedorientation and a deployed orientation, the stent body having acircumference and a longitudinal axis extending between first and secondopen ends; the stent body having a plurality of circumferential supportstructures which extend generally about the circumference of the stent,the circumferential support structures being spaced-apart along thelongitudinal axis and including pairs of tapered struts alternating withsingle, non-tapered struts; each of the circumferential supportstructures including longitudinal struts interconnected at apexportions, at least some of the longitudinal struts having widths thattaper as the at least some longitudinal struts extend along the stentbody longitudinal axis, the longitudinal struts and apex portionsdefining an undulating pattern, at least some of the apex portions ofadjacent circumferential support structures being configured tolongitudinally extend past each other when in the un-deployedconfiguration thus providing longitudinal overlap; and a plurality ofcircumferential connecting struts interconnecting at least some of theadjacent circumferential support structures, the circumferentialconnecting struts extending between the apex portions that extend pasteach other.
 2. The stent of claim 1, wherein the adjacentcircumferential support structures include a first circumferentialsupport structure and a second circumferential support structure that isadjacent to the first circumferential support structure, and wherein inthe deployed orientation, the adjacent circumferential supportstructures are offset such that the apex portions on one side of thefirst circumferential support structure are positioned intermediate theapex portions on a facing side of the second circumferential supportstructure.
 3. The stent of claim 1, wherein at least some of thecircumferential connecting struts have a width greater than a width ofthe longitudinal struts.
 4. The stent of claim 3, wherein the adjacentcircumferential support structures include a first circumferentialsupport structure, a second circumferential support structure and athird circumferential support structure, wherein the secondcircumferential support structure is adjacent the first and the thirdcircumferential support structures, and wherein the circumferentialconnecting struts joining the first and the second support structuresextend in a first direction and the circumferential connecting strutsjoining the second and the third support structures extend in a seconddirection opposite the first direction.
 5. The stent of claim 3, whereinthe undulating pattern defines a wavelength, and wherein thecircumferential connecting members are at feast one half the length ofthe wavelength.
 6. The stent of claim 1, wherein at least same of thecircumferential connecting struts have a width at least twice as greatas a width of the longitudinal struts.
 7. The stent of claim 1, whereinthe pairs of tapered struts are longer than the non-tapered struts. 8.The stent of claim 7, wherein the pairs of longer tapered struts areinterconnected by the circumferential connecting struts.
 9. The stent ofclaim 1, wherein some of the longitudinal struts are longer than otherlongitudinal struts, and wherein the longer longitudinal struts providethe longitudinal overlap at the apex portions.
 10. The stent of claim 1,wherein the circumferential connecting struts extending between the apexportions that extend past each other are angled with respect to thecircumference of the stent body.
 11. A stent comprising: a stent bodyexpandable between an un-deployed orientation and a deployedorientation, the stent body having a circumference and a longitudinalaxis extending between first and second open ends; the stent body havinga plurality of circumferential support structures which extend generallyabout the circumference of the stent, the circumferential supportstructures being spaced-apart along the longitudinal axis and includingpairs of adjacent circumferential support structures; each of thecircumferential support structures including longitudinal strutsinterconnected at apex portions, the longitudinal struts and apexportions defining an undulating pattern, at least some of the apexportions of adjacent circumferential support structures being configuredto longitudinally extend past each other when in the un-deployedconfiguration thus providing longitudinal overlap; and a plurality ofcircumferential connecting members interconnecting only alternatingpairs of the adjacent circumferential support structures, thecircumferential connecting members being located between only some ofthe pairs of the adjacent circumferential support structures andextending between the apex portions that extend past each other.
 12. Thestent of claim 11, wherein some of the pairs of the adjacentcircumferential support structures have apex portions that appose oneanother, and other pairs of adjacent circumferential support structureshave apex portions that are offset from one another.
 13. The stent ofclaim 11, wherein three consecutive circumferential support structuresare interconnected by the circumferential connecting members.